Integral fuel tanks are unique in their structure since they are part of the aircraft's overall supportive shape. These fuel tanks are built into the aircraft's framing. As a result, the tanks cannot be removed for servicing or replacement. Engineers must strategically place the tanks within the aircraft's structure while considering the balance of the fuel's weight, as well as overall fuel volume needs.
The fuel tank's placement determines its type, or shape. The majority of integral fuel tanks reside in the wings. Each wing holds two fuel tanks. The tanks fill the open space between the top and bottom wing surfaces. The fuel tank closest to the airplane's fuselage is almost a perfect square shape, having more room because of the large wing width. As the wing tapers down to the tip, another fuel tank fills this small space in the shape of an oblong rectangle.
Some airplanes require larger fuel reserves, especially for long distance traveling across oceans. These airplanes add extra integral fuel tank types along the fuselage's belly, or underside. Similar to the wing tanks, the belly tank placement resides within the fuselage's permanent body framing, preventing any access to the fuel tank. In addition, the aircraft's tail can house a small integral fuel tank for even more storage. These tank types vary in design and shape, depending upon the overall airplane construction and engineering from the manufacturer.
According to Lockheed Martin, integral fuel tanks offer the best carrying efficiency for fuel. The fuel tanks are not centralized in one area, causing the airplane to have an extreme imbalance. The integral tanks balance the fuel along the airplane's body for stabilizing the entire fuselage structure. In particular, fuel from the wing and belly tanks has a short distance to travel for supplying power to the airplane's engine, increasing fuel distribution efficiency.
All integral fuel tank types must be sealed precisely. Since they are part of the aircraft's structural framing, repairing a leak is extremely difficult. During manufacturing, workers must verify that the tanks are free from any small openings before permanently installing the assemblies, avoiding a costly fuel leak.
